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Articles by G. Ouma
Total Records ( 7 ) for G. Ouma
  E. Luvaha , G.W. Netondo and G. Ouma
  Six month old Mango (Mangifera indica L.) rootstock seedlings were grown in 20 L plastic pots in a greenhouse at Maseno University, Kenya. to investigate the effect of water deficit on its morphological and physiological characteristics such as plant height, number of leaves, stem diameter and gas exchange characteristics and chlorophyll content, respectively. A Completely Randomized Design (CRD) with four treatments and six replications was used. The treatments involved subjecting the rootstock seedlings to four different irrigation regimes namely watering daily, twice in a week, once in a week and once in two weeks. The measurements were taken after every two weeks for a period of three months. At the end of the experiment, destructive sampling to establish the root to shoot ratio were taken. The soil moisture content under the different irrigation regimes was also determined gravimetrically. Growth parameters increased under mild water stress except under extreme water deficit where there was wilting. Root to shoot ratio increased with increasing water deficit. Increase in water deficit reduced the gas exchange parameters but slightly increased chlorophyll content. It is concluded that water deficit significantly (p≤0.05) affects physiological and morphological characteristics of Mango.
  E. Luvaha , G.W. Netondo and G. Ouma
  D.M. Musyimi , G.W. Netondo and G. Ouma
  J. Kaoga , G. Ouma and P. Abuom
  Lake Naivasha and its environs experienced increased levels of pesticide application due to the rapid expansion in floriculture farming. Previous studies had shown detectable levels of Organochlorine pesticide residues in water samples. The Lake is under threat since such occurrences are linked to the poor water quality. Moreover, Organochlorine pesticide residues persist in the environment while, the Organophosphate pesticides which had been adopted as an alternative to Organochlorine pesticides were highly toxic. The study investigated the occurrence and effects of Organochlorine and Organophosphate pesticide residues on water quality. The specific objectives of the study were: To determine water physico-chemical parameters and investigate pesticide residues concentration of Organophosphate and Organochlorine. Longitudinal study design was used during the months of February to July, 2011. The sampling sites were selected on the basis of their relevance as point sources of pesticide contamination. Three replicates of water samples were collected monthly, 18 water samples per site, totaling to 90 samples. These samples were subjected to water quality analysis and Gas Liquid Chromatography technique. The data generated were subjected to analysis while applying Statistical Package of Social Science using one way ANOVA at p<0.05. The results revealed that the water samples tested were in compliance with World Health Organisation and Kenya Bureau of Standards recommended guidelines while, Organochlorine and Organophosphate pesticide residues were not detected. It was concluded that the lack of these pesticide residues was due the current conservation measures preventing water pollution in the Lake. The study further, recommended continuous monitoring and conservation measure to be maintained.
  S. Sikolia , E. Beck , J.I. Kinyamario , J.C. Onyango and G. Ouma
  δ13C values of the Centrospermeae species are presented. 69.5, 28.45, 1.25 and 0.8% of the total species are C3, C4, C3-C4 and CAM photosynthetic species. The δ13C values are species dependent. δ13C values for the C3 range from -21.16 to -30.28‰ while the C4 species vary from -10.60 to -16.55‰. An exceptional δ13C value of -32.28 is reported for Chenopodium capitatum. δ13C value for the CAM species vary from -16.00 to -18.50‰. C3-C4 species includes Mollugo nudicaulis, Portulacaria afra and Portulaca sp. nov. with δ13C values -25.89, -20.93 and -15.66‰, respectively. Temperature and precipitation are the dominant causal climatic factors that influence the distribution of the C3 and C4 species inversely and by extension the δ13C values along the altitude. Other climatic factors act synergistically. A difference in the δ13C values is a biochemical dual function of the Rubisco and suberized lamella anatomical structural organization. The occurrence of some C4 species in the unusual high altitude includes Melandrium nordiflorum and Silene abyssinica and may be due to the Pyruvate Phosphate Dikinase (PPDK) enzyme functional activity. Ecological significances of the δ13C values are discussed.
  Elizabeth Luvaha , G.W. Netondo and G. Ouma
  The present studies were aimed at investigating the effect of different watering regimes on the gas exchange parameters (stomatal conductance, CO2 assimilation and transpiration rates) and chlorophyll content of young Mango (Mangifera indica) rootstock seedlings. The hypothesis was that different levels of water deficit affect the gas exchange parameters and chlorophyll content of the mango rootstock seedlings. Six-month-old Mango (Mangifera indica L.) rootstock seedlings were grown in polythene pots in a greenhouse at Maseno University, Kenya from December 2003 to March 2004 and subjects to four different watering regimes (namely daily, twice in a week, once in a week and once in two weeks). These treatments were in a Completely Randomized Design (CRD) with six replications. The parameters determined were stomatal conductance, transpiration rate, CO2 assimilation rate and intercellular CO2 concentration. All the gas exchange parameters were determined by infra Red Gas Analyser (PP systems). The results showed that increasing water stress reduced the physiological parameters particularly at the later days of plant growth due to stomatal and non-stomatal factors. Leaf chlorophyll content however was slightly increased since the chlorophyll pigments may have been resistant to dehydration. It is concluded that increase in water stress (increasing level of water deficit) reduces the gas exchange parameters of mango (Mangifera indica) rootstock seedlings but slightly increased chlorophyll content due to an adaptive mechanism.
  D.M. Musyimi , G.W. Netondo and G. Ouma
  This study was conducted to investigate growth and gas exchange characteristics of avocado seedlings growing under different salinity levels under naturally illuminated greenhouse conditions, in order to relate this physiological information to the ecology of this avocado cultivar. Plants grown in 4.5 L plastic pots containing soil were subjected to 0 (control), 15, 30, 45 and 60 mM NaCl salinity treatments. The measured parameters started to show significant differences (p≤0.05) by day 7. Interactions between salt treatments and duration of salt exposure were highly significant at p≤0.05. Net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E) and chlorophyll (chl) concentration decreased in response to increasing salt concentration in the growth medium. Water use efficiency (WUE) decreased in all the treatments during the time course of experiment. Substomatal CO2 concentration (Ci) and chloride ions content increased with increasing salt concentration of the growth medium. It is suggested that the greater inhibition of CO2 fixation may be due to impairment of photosynthetic apparatus. Treatment consisting of 60 mM NaCl caused maximum growth reductions. The findings in this study demonstrate that NaCl salinity hampers growth and gas exchange processes of avocado plants and improvement in salt resistance of avocado rootstock under study is more likely to come from increasing further screening of more avocado rootstocks for salt tolerance or resistance.
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